Enterprise Library Configuration breaks LDAP connection string

[Per Bolmstedt]

I'm using the Enterprise Library Configuration tool to manage the
Enterprise Library parts of my Web.config.

I'm also using the
System.Web.Security.ActiveDirectoryMembershipProvider, and I have to
supply it with the name of a connection string defined in
<connectionStrings>. The connection string looks like this:

<add name="AD" connectionString="LDAP://domain.my" />

When ELC saves the .config file, it doesn't recognize this type of
connection string (there's no data source, no provider name etc) so it
justs blanks it, changing it to:

<add name="AD" connectionString="" />

What is the solution to this?

(The only workaround I can think of is setting the membership
provider's connection string at runtime, but I don't know if that's
possible.)